An automotive catalytic converter is an emissions control device that may be incorporated into the exhaust system of a motor vehicle between the exhaust manifold and the muffler. The catalytic converter contains one or more catalysts, such as those based on platinum, palladium, or rhodium, that reduce the levels of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) in the exhaust gas, thereby reducing the amount of these pollutants which would otherwise be emitted into the atmosphere from the vehicle. In a typical commercial catalytic converter, HC and CO in the exhaust are oxidized to form carbon dioxide (CO2) and water, and NOx are reduced to nitrogen (N2).
As a result of recent regulatory initiatives, motor vehicle emissions control devices, including catalytic converters, are now required to have longer useful lives. US regulatory authorities such as the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) now require automotive emission control elements to function up to 150,000 vehicle miles. This requirement, coupled with tighter emission standards, places severe demands on catalytic converters and other exhaust emissions control devices. Catalytic converters lose efficiency primarily by two mechanisms. High exhaust temperatures can cause thermal damage, and a number of components introduced into the typical automotive internal combustion engine exhaust, e.g. from the lubricating oil, can act as poisons to the catalyst present in the converter.
In order to accommodate these stringent EPA requirements, it is important to develop methods for accelerated aging that adequately simulate the impact of various engine operating modes, such as a cold start mode, on the catalytic converter.
In a vehicle, a catalytic converter may experience several thousand cold starts during its lifetime. The conditions experienced by a catalytic converter during an engine cold start in a vehicle may significantly impact aging of the catalytic converter. However, bench engine accelerated aging cycles do not incorporate cold start simulation, and thereby neglect a potentially important aspect of real world catalyst aging. One reason for the omission of cold starts from bench engine aging is that it can take several hours to cool an engine down to near ambient conditions. Including a significant number of cold starts into a bench engine aging cycle would make the overall aging time much too long to be of practical use.
A method is needed to simulate cold starts to more accurately and efficiently assess the impact of cold starts on aging of a catalytic converter.